Techniques have been developed for administering pharmaceuticals through the skin by absorption. Such techniques are accomplished by devices which typically comprise either a pharmaceutical-containing reservoir enclosed by a synthetic membrane through which the pharmaceutical can diffuse at a controlled rate, or a dispersion of a pharmaceutical in a synthetic polymer matrix in which the pharmaceutical can diffuse at a controlled rate. While such delivery devices work for some pharmaceuticals, the rate of release of other pharmaceuticals is not adequate through synthetic polymers. Either the rate of delivery is too slow to provide an effective dosage given the area of the delivery surface, or in some cases, where prolonged delivery of the drug is desired, delivery is too fast so that the device must be replaced within a short period of time. One situation in which it is desirable to have a drug delivered over a prolonged period of time without removal of the delivery device is the case of delivery of drugs at a wound site around a percutaneous medical device.
Moreover, it is desirable, particularly when dealing with delivery of bioactive agents which are natural products, such as growth factors, that the polymeric matrix from which the drug is delivered be tailored for optimal drug delivery rate. It is difficult to do this when the drug to be delivered is a biological macromolecule, such as an enzyme or surface receptor, since specialized binding functionalities with proper charge density, orientation, hydrophobic domains, etc. are not readily synthesized into synthetic polymers to release the biological macromolecule at a desired controlled rate.
It is thus an object of the present invention to provide a polymeric delivery compositions for controlled release of bioactive agents, particularly biological macromolecules, which is formed of a foam composite of a biopolymer and a synthetic polymer.
It is another object of the present invention to provide drug delivery devices, particularly wound dressings, containing such polymeric delivery vehicles for controlled release of antimicrobial and/or wound-healing agents to aid in the wound healing process.
It is another object of the present invention to provide a catheter-securing and drug delivery device which is easily used which contains a pad comprising a biopolymer which serves as a delivery vehicle for controlled release of a bioactive agent to the catheter wound site.
These and other objects of the invention will be apparent from the following description and appended claims, and from practice of the invention.
The present invention provides a method for preparing a polymeric delivery vehicle for controlled release of a bioactive agent. The method comprises the steps of cross-linking a biopolymer which contains chemically reactive functionalities which react with a cross-linking reagent, where the cross-linking agent comprises greater that two reactive sites per molecule which are chemically reactive with functionalities on the biopolymer, to form a cross-linked biopolymer; optionally, forming the cross-linked biopolymer into a desired shape; then contacting the cross-linked biopolymer with a bioactive agent to reversibly bind the bioactive agent to the biopolymer to form the polymeric delivery vehicle. Preferably, the cross-linking reagent is a polyurethane or polyurethane urea having isocyanate side groups and/or end groups. It will be appreciated that the number of reactive sites per molecule of the cross-linking agent is a statistical average, therefore some cross-linking molecules will contain two or less reactive sites. Alternatively, the bioactive agent is bound to the biopolymer before treatment with the cross-linking agent. By effective binding affinity it is meant that the bioactive agent can be bound (noncovalently) to sites in the biopolymer; then, when in use in contact with skin and/or bodily fluids, or other fluids, a substantial amount of the bioactive agent will be released from the biopolymer, with release sustained for a period of time, controlled by the binding affinity.
As used herein, the term xe2x80x9cbinding affinityxe2x80x9d is the ratio of the amount of bound drug (the bioactive agent) to the amount of free drug, wherein
[Bound drug]=[the total amount of drug found in a biopolymer sample which is contacted with a solution of drug and allowed to equilibrate] minus [the volume of solution absorbed by the biopolymer times the concentration of drug in the remaining unabsorbed solution]
[Free drug]=[the total amount of drug found in the biopolymer sample] minus [Bound drug].
Thus,       Binding    ⁢          xe2x80x83        ⁢    affinity    =                    [                  Bound          ⁢                      xe2x80x83                    ⁢          drug                ]                    [                  Free          ⁢                      xe2x80x83                    ⁢          drug                ]              =                  [                  Bound          ⁢                      xe2x80x83                    ⁢          drug                ]                              [                      Total            ⁢                          xe2x80x83                        ⁢            drug                    ]                +                  [                      Bound            ⁢                          xe2x80x83                        ⁢            drug                    ]                    
Generally, a higher binding affinity provides a longer sustained release of drug. Particularly preferred compositions have binding affinities over 0.8, preferably 1.0 and higher. Useful compositions have a binding affinity for the drug in the range of 1.0 to 5.0.
In a preferred embodiment of the present invention, the polymeric delivery vehicle is used in a catheter-securing and drug delivery device. The device comprises an elastomeric pad having a radial slit extending from the edge of the pad to a central point proximate to the center of the pad. The pad comprises a cross-linked biopolymer and a bioactive reagent reversibly bound thereto, wherein the bioactive reagent is releasable from the cross-linked biopolymer in a controlled manner to a wound or to the skin. The device further comprises a reinforced, flexible, water vapor permeable membrane adhesively attached to the pad which extends beyond the edge of the pad on all sides thereof, thereby forming a flange surrounding the pad. At least the edges of the exposed bottom surface of the membrane is coated with an adhesive material for affixing the device to the skin. The membrane has another radial slit extending from the edge of the membrane, through the membrane toward the central point of the pad, which is colinearally aligned with the slit in the pad. Finally, the device optionally comprises a reinforced, flexible, water vapor permeable tab affixed to the upper surface of the membrane and located proximate to one side of the pad wherein one surface of the tab is adhesively coated and the tab has dimensions sufficient to cover the pad when the tab is folded for adhesive attachment to the upper surface of the pad.
In another preferred embodiment the polymeric delivery vehicle in the form of an elastomeric pad is used as a wound dressing. The pad may be secured upon a wound by an adhesive water-vapor film over the pad which adheres to the skin area surrounding the wound.